This invention relates to a mineral mining plough for winning material in a mineral mining working. The invention is particularly concerned with a plough for winning different amounts of material on the "uphill" and "downhill" runs, that is to say, a plough utilising the method of asymmetrical ploughing. Throughout this specification, the term "uphill" run should be taken to mean the ploughing run whose direction is opposed to that of the conveyor along which the plough moves, and the term "downhill" run should be taken to mean the ploughing run whose direction is the same as that of the conveyor.
Asymmetrical ploughing has been well known since it was realised that, because of better ploughing techniques on the downhill run, a coal plough can win considerably more coal than the conveyor is capable of removing. Obviously, this depends on the consistency of the coal and other operating conditions. The conveyor can remove only a comparatively small amount of coal on the downhill run because the conveyor and the plough move in the same direction (with identical speeds the conveyor will be completely overloaded at one point, because the downhill moving coal stream would always be discharged at the same place onto the conveyor). The obvious way of getting round this problem is to increase the plough speed to such an extent that it exceeds the speed of the conveyor and so leads to a more favourable loading of the conveyor. Even then, however, it is not possible, during the downhill run, to utilise the optimum depth of cut of the coal plough. On the other hand, on the uphill run, it is possible for the plough to utilise the optimum depth of cut. This is because the plough and conveyor have a very high relative speed (the conveyor moving in the opposite direction to the plough). The consequence of this is that coal, which theoretically could be mined, is abandoned solely because the conveyor is not capable of removing this coal on the downhill run.
A mineral winning plough has been proposed having a first set of cutters arranged to win material lying a first height range, and a second set of cutters arranged to win material lying in a second height range. The plough is driven on the downhill run with the cutters so positioned that material is won to a greater depth over the first height range than over the second height range. The plough is then driven on the uphill run with the cutters so positioned that material is won to a smaller depth over the first height range than over the second height range.
With the plough, it is possible so to work a coal face to the correct profile that not only is the conveyor substantially uniformly loaded, but also the plough drive can be operated using substantially the same power during both uphill and downhill runs. In order to equalise the power requirements for the two runs, as well as to utilise as completely as possible the available drive capacity, the first set of cutters (which is pivotally mounted on the plough body for lateral movement into, and out of, its working position), is adjusted on the downhill run to a depth of cut that is considerably greater than that of the other cutters effective on the downhill run. For example, the first set of cutters may be adjusted to have the same depth of cut on the downhill run as the second (main) set of cutters on the uphill run. Usually, the first set of cutters are floor cutters so that a stress-relief cut is made at floor level on the downhill run, the stress relief cut facilitating the winning of coal in the subsequent uphill run.
The disadvantage of this plough is its length which results from the lateral pivoting of the first set of cutters, prevents the plough winning material at the ends of its two runs. The aim of the invention is, therefore, to provide an efficient plough of the shortest possible length which is suitable for asymmetrical ploughing.